The disclosed invention is directed generally to a head-up holographic virtual image display, and is more particularly directed to a dynamic holographic virtual image instrument display for a vehicle.
Head-up holographic instrument displays for vehicles, which provide virtual images that appear to be located ahead of the vehicle windshield toward the front of the vehicle, provide the advantages of increased safety since the operator does not have to significantly divert attention from viewing the outside, and are more readily noticed in the event of the display warning of a malfunction.
Known head-up displays include "static" displays wherein predetermined message holograms (e.g., "low fuel") in a vehicle windshield are selectively illuminated by appropriate light sources. The obvious problem with such static displays is their inability to indicate changing parameters such as vehicle speed or engine speed.
Known head-up displays also include "dynamic" displays wherein the visible image is changeable. An example is the use of individual hologram segments in a vehicle windshield which are selectively illuminated by respective beams to control the visibility of the individual segments to display changing numerical information, for example. However, the use of hologram segments provides low image resolution, and is subject to ambient scatter and ambient turn-on (i.e., the unintended "turn-on" of the hologram image caused by an ambient light source). Ambient turn-on is a particularly important consideration since erroneous readings will occur, which could be potentially dangerous depending on the displayed information. Further, since the illuminating light sources would have to be carefully aligned and maintained in alignment, this dynamic display is complex, expensive, and subject to potential reliability problems.